Drilling well bores in the earth, such as well bores for oil and gas wells, is an expensive undertaking. One type of drilling system used is rotary drilling, which consists of a rotary-type rig that uses a sharp drilling tool at the end of a drill string to drill deep into the earth. At the earth's surface, a rotary drilling rig often includes a complex system of cables, engines, support mechanisms, tanks, lubricating devices, and pulleys to control the position and rotation of the bit below the surface. Underneath the surface, the drilling tool is attached to a long drill string that transports drilling fluid to the drilling tool. The drilling fluid lubricates and cools the drilling tool and also-functions to remove cuttings and debris from the well bore as it is being drilled.
Directional drilling involves drilling in a direction that is not necessarily precisely vertical to access reserves. Directional drilling involves turning of the drilling tool while within the well bore. Offshore drilling often involves directional drilling because of the limited space beneath the offshore platform, although directional drilling is also vastly used onshore.
Various types of directional drilling tools exist. One type of directional drilling involves rotary steerable directional drilling, in which the drill string continues to rotate while steering takes place. Typically, a plurality of steering ribs are associated with the rotary steerable tool to facilitate the steering. The ribs are disposed outwardly from a sleeve, inside of which is disposed a rotating shaft associated with the drill string. In one type of rotary steerable tool, the outer sleeve rotates and in another the outer sleeve does not rotate. In the type in which the outer sleeve does not rotate, bearings allow relative movement between the outer sleeve and the rotating shaft. High axial and torsional forces are often encountered during this type of drilling.